Fresh-cut, green tobacco has virtually no nitrosamine carcinogens. See Wiemik et al., “Effect of Air-Curing on the Chemical Composition of Tobacco,” Recent Advances in Tobacco Science, Vol. 21, pp. 39 et seq., Symposium Proceedings 49th Meeting Tobacco Chemists' Research Conference, Sep. 24-27, 1995, Lexington, Ky. On the other hand, cured tobacco is known to contain a number of nitrosamines, including the harmful carcinogens N′-nitrosonomicotine (NNN) and 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK). However, fresh-cut green tobacco is generally considered unsuitable for smoking or other consumption.
Tobacco-specific nitrosamines (TSNAs) are formed primarily during the curing process. It is believed the amount of tobacco-specific nitrosamine (TSNA) in cured tobacco leaf is dependent on the accumulation of nitrites, which accumulate during the death of the plant cell and are formed during curing by the reduction of nitrates under conditions approaching an anaerobic (oxygen deficient) environment. The reduction of nitrates to nitrites occurs by the action of micro flora on the surface of the leaf under anaerobic conditions, and this reduction is particularly pronounced under certain conditions (e.g., humid conditions). During the curing process, the tobacco leaf emits carbon dioxide, which can further dilute oxygen levels in the environment. Once nitrites are formed, these compounds are believed to combine with various tobacco alkaloids, including pyridine-containing compounds, to form nitrosamines.
Williams U.S. Pat. No. 6,202,649, to the present inventor, describes a method of substantially preventing formation of TSNA by, among other things, curing tobacco in a controlled environment having a sufficient airflow to substantially prevent an anaerobic condition around the vicinity of the tobacco leaf. The controlled environment is provided by controlling one or more curing parameters, such as airflow, humidity, and temperature. In practice, Virginia flue tobacco curing according to the method described in Williams '649 typically has a content of N′-nitrosonornicotine (NNN) up to about 0.05 μg/g, a content of 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) up to about 0.05 μg/g, and contents of N′-nitrosoanatabine (NAT) plus N′-nitrosoanabasine (NAB) up to about 0.1 μg/g. Although these TSNA levels are dramatically lower than levels obtained using other curing methods, in some cases it may be desirable to obtain even lower TSNA levels, such as for tobacco used in smokeless products or pharmaceuticals that are orally ingested.